1. Field of the Invention
The present invention relates to production method of dielectric ceramic composition and production method of electronic device. The present invention further particularly relates to production method of dielectric ceramic composition, capable to improve breakdown voltage and lifetime characteristic as well as good specific permittivity, dielectric loss and capacitance-temperature characteristic, and production method of electronic device.
2. Description of the Related Art
A multilayer ceramic capacitor, an example of electronic devices, for example, is manufactured by firing a green chip obtained by stacking alternately ceramic green sheets comprising pre-determined dielectric ceramic composition and internal electrode layers in a pre-determined pattern to be integrated. Since the internal electrode layer of multilayer ceramic capacitor is integrated with the ceramic dielectric body by firing, a material not reacted with the ceramic dielectric body needs to be selected. Therefore, as a material constituting the internal electrode layer, there has been no choice but using expensive noble metal such as platinum and palladium.
On the other hand, dielectric ceramic composition wherein inexpensive base metal such as nickel and copper can be used has been recently developed to attain significant cost reduction. Among such dielectric ceramic compositions, for example, Japanese Unexamined Patent Publication 2004-107200 (patent article 1) proposes dielectric ceramic composition comprising a main crystal particle consisting of perovskite-like composite oxide including Ba, Ti, rare-earth element, Mg and Mn, and two-sided grain boundary phase and triple point grain boundary phase formed by the main crystal particle, wherein in the triple point grain boundary phase, at least M4R6O(SiO4)6-type crystal phase (M is at least one element selected from alkaline earth elements and “R” is at least one element selected from rare-earth elements) is precipitated. An object of the patent article 1 is to provide a dielectric ceramic composition with high breakdown voltage and good capacitance-temperature characteristic even when using it for a thin dielectric layer with a thickness of 3 μm or less.
In the patent article 1, a composition having the above constitution is in particular manufactured in the following method. Namely, the surface of raw powder comprising of BaTiO3 is first coated with oxides of rare-earth element, Mg and Mn, to prepare coated BaTiO3 powder; then, to the coated BaTiO3 powder, powder including oxides of alkaline earth elements and Si (SiO2) is mixed to obtain dielectric powder; and the obtained dielectric powder is fired in a reduced atmosphere, followed by heat treatment under an atmosphere with higher oxygen concentration than the reduced atmosphere.
Particularly, the patent article 1 discloses that by employing such a production method, the M4R6O(SiO4)6-type crystal phase can be precipitated uniformly in the triple point grain boundary phase. However, the patent article 1 allows improving breakdown voltage, but improvement in lifetime characteristic is insufficient, resulting in lower reliability.